Generally, cultivation using seawater may be largely classified into a land-based aquarium farming and an underwater fish farming. The land-based aquarium farming is to move target organisms to a water tank on the ground and cultivate the organisms while artificially adjusting inhabited environment, and the underwater fish farming is to cultivate target organisms while enclosing the organisms with nets or the like in wide areas in the sea. The use of the underwater fish farming tends to increase because the underwater fish farming need not replace seawater, as opposed to the land-based aquarium farming, and can cultivate fish in large quantities. In the underwater fish farming, persons directly scatter feed in the sea in a spraying or throwing manner.
However, in the underwater fish farming, the manual feed supply is almost impossible when weather conditions are bad. When the underwater fish farming is performed in the ocean far away from the ground, persons have to move a long distance everyday.
In addition, since feed is manually supplied, large-size fish farms require a lot of workers. Thus, a lot of money is spent in cultivation of fish. Moreover, since feed must be supplied everyday, a person cannot leave the fish farm for a long time.
The feed supplied by a person floats in the sea for a predetermined time, absorbs water, and then deposits on the seabed. Thus, a large amount of feed is washed away while fishes do not eat the feed. As a result, feed is unnecessarily wasted and seawater is polluted by the wasted feed.